How to use interactive LightMix?


Interactive LightMix is unique to Corona Renderer and lets you adjust intensity and color of your lights and light emitting materials during and after render – perfect for anything from subtle adjustments through to turning day into night.






What is interactive LightMix?


Interactive LightMix is a new feature introduced in Corona Renderer 1.5, which allows for rendering an image just once, and then changing colors and intensities of the lights directly from the Corona VFB. It can be used after the rendering is finished, and also, like any other post processing in Corona, during the rendering (be it regular or interactive mode). In Corona Renderer 1.6 the LightMix has been additionally improved with:

  • Possibility to bake LightMix parameters into the scene lights and light emitting materials (>Scene button)
  • Better automatic creation dialog with different ways to group lights, information on RAM usage, and checkboxes for denoising and considering hidden lights
  • Better, more user-friendly UI


LightMix can be used on Corona EXR files outside of any 3D software using the Corona Image Editor.





Where to find it? 


LightMix can be set up either automatically, or manually.


To set up LightMix automatically:

Simply go to Render Setup > Scene and under "General Settings" press the "Setup Interactive LightMix" button. Corona Interactive LightMix Setup dialog will then pop up, allowing you to:

  • Choose the way lights are grouped - based on instances, groups, or individual lights. 
  • See how much RAM will be used by each LightMix layer
  • Decide whether hidden lights should be also considered by the LightMix setup
  • Decide whether denoising should be applied to all LightMix and LightSelect render elements


Corona Interactive LightMix Setup window



Once the settings are confirmed with the "generate" button:

  • One CShading_LightMix element will be automatically added to enable LightMix option in the VFB
  • One CShading_LightSelect element will be added with the environment lighting included - this will allow changing the color and intensity of scene environment
  • Multiple CShading_LightSelect elements will be automatically added  - this will allow changing the color and intensity of each scene light


A list of automatically generated LightMix and LightSelect render elements




After using this one-click solution, you can simply start rendering the scene (both regular and interactive rendering will work), and then go to LightMix tab in Corona VFB to change intensity and color of each light:


After using the automatic setup, LightMix tab in the Corona VFB becomes available



To set up LightMix manually:

  1. Go to Render Setup > Render Elements, and then:
  2. Add at least one CShading_LightMix render element - this is required to enable the LightMix option in the VFB
  3. Add at least one CShading_LightSelect render element - this is required to be able to control a scene light, or scene environment


CShading_LightMix and CShading_LightSelect render elements can be added manually



Each light that you wish to control should be added to "Included light sources" list in each CShading_LightSelect render element. You can add one or more lights to each LightSelect element. Additionally, you can check "Include Environment Light" checkbox to control environment lighting.




LightMix and Denosing


You can decide whether denoising should be applied to each LightSelect render element. To denoise the whole LightMix output, you must turn on the denoising option for all LightSelect elements:

Denoising can be enabled manually for each of the LightSelect elements



Denoising can be also enabled automatically for all LightSelect elements using the "included in denoising" checkbox in the Corona Interactive LightMix Setup dialog:

Denoising can be enabled automatically for all of the LightSelect elements


To learn more about denoising, see: What is denoising?




How to use it?


After setting up LightMix (either automatically, or manually), the color and intensity of each light can be changed in the VFB. Simply go to LightMix tab in Corona VFB and change the desired parameters - this can be done during, or after rendering, for both regular and interactive rendering:


After setting up the Interactive LightMix, its dedicated tab in the VFB becomes available




You can also use additional buttons below the lights list:



  • >Scene - This bakes all LightMix colors and intensities into the scene lights. After clicking this and confirming, the image displayed in the VFB will be temporarily changed to the non-LightMix version, and you will need to re-render it to get the desired result. Lights which are instanced will become unique in case some of them were separately altered using the LightMix.

  • Save... / Load... - This saves a LightMix preset as a .conf file. Useful, for example, when creating day and night versions of a scene. It is also possible to load a preset after a camera is changed and a different view is rendered. The .conf files can be also loaded into the Corona Image Editor.

  • Toggle all - This enables or disables all lights in the LightMix list.

  • All 1.0 - This reverts all LightMix layers' intensities to 1.0, which means the values set in the scene will be used - this will NOT make all lights equally bright if they have different intensities set in the scene.

  • All white - This simply reverts the colors of all LightMix layers to pure white, which results in having the initial colors of scene lights used.




What are the limitations?


There are some technical limitations when using LightMix:


  • Using extremely high or low light intensities
    This, depending on the intensity, may result in persistent noise (fireflies).
    Solution: after setting the LightMix as desired, use the >Scene button in the VFB LightMix tab to bake your settings into the scene.

Using extremely high or low light intensities in the LightMix always leads to excessive noise.


  • Adding a lot of lights and rendering in very high resolution
    This can lead to excessive RAM usage. A warning message should appear when attempting to set up LightMix with many lights.
    Solution: render your image in low resolution to keep memory usage low, then adjust LightMix settings as needed. Once the LightMix setup is complete, use the >Scene button to bake all custom light settings into the scene, then disable all LightMix and LightSelect render elements, and re-render your image in high resolution. This way you will be able to use your LightMix settings in a high-resolution render, without the high RAM usage.

  • Using the ShadowCatcher material
    LightMix does not interactively update shadow catcher material shading results - this is currently a limitation.
    Solution: use the >Scene button to bake LightMix properties into the scene. Then re-render your image and use the beauty pass to get the correct ShadowCatcher result. 
    See: Known bugs and limitations

    Beauty render element:

    LightMix result:


Other than that, the results of using LightMix are only limited by your imagination. :)